You can wirelessly control your garage door, car, sprinkler system, and other everyday items with a Bluetooth board and a free Android app (or Bluetooth workaround for other mobile operating systems). Instructables user tcollinsworth shows us how.
You basically need a Bluetooth board (the one recommended is $US55), a MOSFET switch (a transistor that ensures power is turned off), and a few other inexpensive materials and tools. Tcollinsworth provides very informative diagrams and instructions on how the parts all work together, e.g. how you can control your garage door with your mobile phone.
A free Android app, Daisy On/Off, provides the interface in this example for controlling the Bluetooth-enabled garage door and car starter.
If your phone is the main thing you have with you at all times, this may be a very worthwhile weekend project.
Bluetooth Garage Door Opener & Car Starter [Instructables]